99 EXPY 5.4 OBDII code P0171
 

Hello everyone,

Ok I have a 99 expy with 233,000 miles. Got here with 130K and she has giving me not one problem with regular service and maintenance until now. For the second time I am getting CEL steady on (not blinking). When I run the OBD II I get code Po171 Bank 1 System Lean. The first time I got it (last year in the summer) I cleaned the MAF, installed a new fuel filter, checked the PCV Valve, and did an oil change. The code cleared but returned again last week friday. I did the same as before (cleaned the MAF, installed a new fuel filter, checked the PCV Valve) except no oil change yet (it's due now. I do it every 3K). The PCV valve seems to be fine the MAF is clean doesn't look to be bad. NO I have not done a smoke test to see if there is a leak some where. Can any one give some advice or help norrow down the couse for this code. It is the only code I am getting although I found a stored code in the on board memory (P230 & P1464) which I never got on an active scan only in the DTC continuous memory scan. Help!!! I really am not prepared to spend $500 to fix this.

You narrowed it down to one side by the code at least. Your issue is on bank 1 so where number 1 spark plug is. Is where you are looking on that bank. If u have a scanner that will do pid streaming you need to look at your short fuel trims and long fuel trims to get a better idea when this issue is happening. Visually check all your hoses for any collapsed or pinched ones. May be an intake gasket leak

The most likely cause is a vacuum leak.
Check all vacuum hoses for leaks. Listen for hissing sounds, pinch off hoses to listen for idle changes use carb cleaner of propane gas as enrichment tools....

I ran across this:
1998 Ford Expedition Vacuum Assembly

Yes there is a hissing type noise but I can't locate it. I have been trying to figure out how to smoke test. Don't really want to pay a shop to do it.

Bluewind

Thanks for the link and the video. They were both very informative and helpful. I think I found the leak location. Sounds like its under intake manifold cover. Will try to tackle this this weekend.

OK update good news. There was a leak in the PCV hose that connects in t he rear of the manifold. I got the old hose off but the tube was so old/Dry it broke off. Now I can't get the boot off. Any Ideas cause now I'm stuck without a vehicle?

if the boot is connected to a steel tube on the intake...run a pick, with a 90 degree bend, between the tube and boot....this will separate the stuck boot, then twist and pull off.


great video bluewind.

you can rule out vacuum leaks from the inside of your car using only a scan tool.
if the fuel trim is adding fuel at idle but drops back to normal at 2500rpm a vacuum leak is present.
if the fuel trim is still adding at 2500rpm, its not a vacuum leak. The false air from the vac leak is insignificant at higher rpm due to the large volume of incoming air and drop in manifold vacuum.

tribeone, primem, FordLifeSaver:

This has become a cool thread. Everyone contributes and everyone learns.